1. Field of the Invention
This invention relates to the improvement of a double super tuner suitable for reception of CATV (Cable Television) broadcast, satellite broadcast, and HDTV (High Definition Television) broadcast in the UHF (Ultra High Frequency) band or the like, for example.
2. Description of the Related Art
As is well known in the art, a double super tuner is constructed as shown in FIG. 1. In FIG. 1, a reference numeral 11 denotes an input terminal which is supplied with an RF (Radio Frequency) signal obtained by receiving the broadcast. The RF signal supplied to the input terminal 11 is supplied to a wideband BPF (Band Pass Filter) 12 which permits passage of signals of entire reception frequency band, amplified by an RF amplifier circuit 13, and then supplied to a first frequency converter circuit 14.
The first frequency converter circuit 14 frequency-converts (up-converts) the input RF signal into a corresponding first intermediate frequency signal based on a local oscillation signal output from a first local oscillation circuit 15. As the first frequency converter circuit 14, a balanced-output type frequency converter circuit is generally used. Therefore, first intermediate frequency signals are output in a balanced state from the first frequency converter circuit 14.
The first intermediate frequency signals output in the balanced state from the first frequency converter circuit 14 are converted into an unbalanced signal by a balanced-unbalanced conversion transformer 16 and then supplied to an unbalanced-input type BPF 17 for first intermediate frequency for effecting the band-pass filtering process for the first intermediate frequency band. The first intermediate frequency signal output from the unbalanced-input type BPF 17 for first intermediate frequency serially passes through a first intermediate frequency amplifier circuit 18 and BPF 19 for first intermediate frequency which are designed for the first intermediate frequency band and is then supplied to a second frequency converter circuit 20.
The second frequency converter circuit 20 converts the input first intermediate frequency signal into a corresponding second intermediate frequency signal based on a local oscillation signal output from a second local oscillation circuit 21. The second intermediate frequency signal output from the second frequency converter circuit 20 serially passes through a second BPF 22 for second intermediate frequency and second intermediate frequency amplifier circuit 23 which are designed for the second intermediate frequency band and is then derived from an output terminal 24.
As shown in FIG. 2A, for example, the above double super tuner has an insertion component 26 such as an air-core coil and various types of on-surface mounting components 27 which are mounted on a printed circuit board 25. In this case, the printed circuit board 25 has circuit patterns 25a formed on both surfaces thereof. The insertion component 26 is inserted from the front surface side of the printed circuit board 25 to the rear surface side and connected to the circuit pattern 25a on the rear surface by solder 28 together with the on-surface mounting components 27.
For soldering the circuit pattern 25a and on-surface mounting components 27 formed on the front surface of the printed circuit board 25, a reflow soldering process is used. Further, as shown in FIG. 2B, the printed circuit board 25 having various types of insertion components 26 and on-surface mounting components 27 mounted thereon is set in a shield case 29 and circuit blocks thereof are separated by use of shield plates 29a so as to attain isolation between the circuit blocks.
It is, however, desirable to improved upon the conventional double super tuner, to simplify circuit construction and enhance performance. In an effort to do so, various studies and developments have been made.